High frequency receiver



Sept. 19, 1939. G. 'w. i-YLER HIGH FREQUENCY RECEIVER Filed July 14, 1937 mrznnabmr:

FREQUENCY AHFLI HER r ur hxwnrypfi 7 3 AMPLIFIER Inventor: Gefge W. Fiyl r, y His Attorney.

Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE HiGH FREQUENCY RECEIVER George W. Fyler, Stratford, coma, assignor to General Electric Company, a corporation of New York Application July 14, 1937, Serial No. 153,573

11 Claims.

the oscillator frequency is automatically tuned to the desired frequency and remains tuned substan'tially to that frequency during movement of the tuning control through a certain small range in the region of that position. Thus irrespective of where in this range the tuning control is positioned the local oscillator is correctly adjusted to produce substantially the frequency to which the intermediate frequency circuits are tuned. Such means, in addition to facilitating tuning, operate also to compensate for variations which may occur in the frequency of the local oscillator. Such variations may occur, for example, during the warm up period. Suchmeans also vary the tuning of the local oscillator thereby to maintain a proper intermediate frequency during variations in the carrier frequency of the received signal if such variations occur.

Such means as now commonly employed are utilized principally in" the broadcast band. One of the objects of my invention is to provide means to facilitate the application of such means to the short wave bands as well.

One of the means commonly employed to effect the desired frequency control comprises an electron discharge device connected to the oscillator in such a way as to act as a variable reactance controlling the oscillator frequency, the varia tion in reactance being effected by variation of the voltage between the grid and cathode. One of the objects of my invention is to provide means whereby a discharge device employed in this way in a. low frequency band may also be employed to effect automatic frequency control in a high frequency band, without limiting the stability of the oscillator, the frequency range over which it operates in the high frequency band, Or producing other undesired effect. A further object is to accomplish this result without material complication of the circuits and switching means employed.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objectsand advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure represents an embodiment of my invention.

7 Referring to the drawing I have shown therein a high frequency receiver comprising an antenna a radio frequency amplifier 2 a first detector 3 an intermediate frequency amplifier 4, a frequency discriminating network 5, and a second detector 6 including load'res'isto'rs I, 8, and 9. A potentiometer H) is connected in a shunt path across resistances 8 and 9 and the audio output of the receiver is taken from conductors II connected to said potentiometer, these conductors extending, for example, to an audio amplifier, or other load circuit, as desired.

As shown in the drawing, the first detector is of the ordinary peritagrid type now commonly employed in radio receivers. This device comprises five electrodes between the cathode and anode at different distances from the cathode, the electrode nearest to the cathode being employed as the grid of the local oscillator and the second electrode from the cathode being employed as the anode of the local oscillator. The fourth electrode from the cathode is employed as the signal input grid, this grid being connected to the output of the radio frequency amplifier 2.

The third and fifth electrodes are employed as screen grids to shield the input signal grid from the local oscillator electrodes and from the anode. These third and fifth grids are connected to a source of positive potential which in the drawing is indicated by' a resistance l2, this resistance comprising, for example, the bleeder resistance of the ordinary power supply system, the cathode of the pentagrid converter being connected to the ground point conventionally indicated on said bleeder". Anode operating potentials for the intermediate frequency amplifier 4, pentag'rid converter 3, and radio frequency amplifier 2 are supplied thereto through conductors l3, I4 and I5 respectively, the anode of the oscillator, that is the second electrode from the cathode of the pentag'rid converter being supplied with anode operating potential through a switch IS in any of its three positions, coil I1, l8 or 19 dependerit upon the position of the switch I6,

resistance 20 and conductor 2| to the positive terminal of the bleeder resistance l2.

The grid of the oscillator is connected to the cathode through a grid leak 22 and also through a path comprising grid condenser 23, switch 24 sistances in any one of its three positions, and thence through coil 25, 25, or 2l, dependent upon the position of the switch, and associated condenser 23, 29 or 38 respectively, to ground.

Coils El and 25 constitute a coupling between the anode circuit of the oscillator and the grid circuit of the oscillator when the switches l5 and 24 are in their righthand position. This position of the switch connects the receiver for operation in the broadcast band. The tuning condenser for the oscillator is indicated at 3! and is arranged for unicontrol with the condensers of the radio frequency amplifier 2 and input to the pentagrid converter, this condenser cooperating with the inductance of the. winding 25 to,

produce the frequency determining circuit of the oscillator for the broadcastband- This circuit, of course, includes the padding condenser 28 and trimming condensers 32 and 33.

With the switches in the position shown the oscillator coupling comprises the transformer including coils 28 and 18, the oscillating circuit of course comprising the coils 2B and the condensers 3i and 32. With the switch in this position the receiver is adapted for operation over a higher frequency band. With the switches 24 and it in their lefthand position the oscillator coupling comprises the coils 21 and 19, the circuits otherwise being as last described. In this position the receiver is adjusted for operation in a still higher, or short wave band.

Of course, similar switches for effecting the band changing function in the circuits of the radio frequency amplifier and first detector signal input are employed, but, for simplicity of the drawing, are not illustrated.

The second detector 8 of the receiver comprises two diodes 35 and 36 which may suitably be arranged within the same envelope and between the cathodes of which the load resistances 1, 8 and 9 are connected in a series circuit. The

cathode of diode 38 is grounded and the cathode 'of diode 35 is connected to conductor 48 the potential of which is utilized to control the frequency of the local oscillator in the manner shortly to be described. The anodes of these two diodes are connected to the opposite terminals of one winding 3'! of a three-winding intermediate frequency transformer 31, 38, 39. The winding 39 is connected in the anode circuit of the last intermediate frequency amplifier. The winding 38 is connected between the midpoint of the winding 37 and the midpoint of the diode load resistances l, 8, 9, through resistance 5!, this midpoint being the point between reand 8. Capacitors between ground and the opposite terminals of resistance 5| and between ground and conductor 48 serve to prevent intermediate frequency currents from appearing on the diode load resistors and on conductor 40.

Windings 31 and 38 are tuned to the intermediate frequency by condensers 52 and 53 and the voltage of winding 3'! is, therefore, displaced by from the voltage of the winding 38 when the intermediate frequency is of the value to which these windings are tuned. The voltages applied to the two diodes 35 and 36 are then equal in magnitude. This causes the undirectional potential on resistance 1 to equal that on resistances B and 9 and since these voltages oppose each other the conductor 48 is at ground potential.

This 90 phase relation, however, between the voltages of windings 31 and 38 exists only when the intermediate frequency is of the correct value, the phase of the voltage of the winding 31 shifting in one direction if the frequency increases and shifting in the opposite direction when the frequency decreases. Thus, for example, if upon a frequency increase the voltage of the winding 38 shifts in one direction, the voltage of the upper half of winding 31 approaches the aiding relation with respect to the voltage of the winding 38 and that on the lower half of winding 31 approaches the opposing relation to the voltage on the winding 38. Thus the voltage applied to diode 35 is increased and that applied to diode 35 is decreased. The potential on resistance 1, therefore, increases and that on resistances 8 and 9 decreases. This in turn causes the automatic frequency control conductor 48 to become positive with respect to ground.

If, on the other hand, the intermediate frequency decreases, then the opposite effect occurs, the potential applied to diode 36 increasing and the potential applied to diode 35 decreasing with the result that the unidirectional voltage on resistances 8 and 9 increases and that on resistance 7 decreases. Automatic frequency control conductor 46 then becomes negative with respect to ground.

The frequency of the'oscillator is regulated by the potential on the automatic frequency control conductor 40 by means of a control electron discharge device 4! having a grid, an anode and a cathode. The grid of this discharge device is connected to the automatic frequency control conductor 40 through resistances 42 and 43. The cathode of this discharge device is connected to ground through a bias resistor 44 and bypass condenser 45. -The cathode is also connected through resistors 54 and 46 to a point of positive potential on the bleeder resistance l2 thereby to produce a constant current in resistance 44 thereby tending to stabilize the bias voltage on the grid of discharge device 4|.

The anode cathode circuit of discharge device 4! includes the winding [1, the resistances 20 and 45 and the source of operating potential [2, the winding 11 of course, during operation in the broadcast band supplying oscillator voltage between the anode and cathode of discharge device H. The portion of the oscillator voltage which appears upon the padding condenser 28 is supplied to the grid of the control electron discharge device 4! through a circuit comprising condensers 47 and 48, resistance 42 and condenser 49. In this circuit the condenser 49 is of the conventional bypass type having large capacitance and hence no material effect upon the phase of the voltage applied to the grid. Condenser is common to the anode circuit of the oscillator and to the above-traced circuit for the grid of discharge device 4|. It is proportioned to produce uniformity of response of the oscillator frequency to variation of potential applied to the automatic frequency control conductor 40, as more particularly described and claimed in copending application Serial No. 147,059, filed June 8, 1937 by Norton F. Shofstall entitled Control circuits and which is assigned to the same assignee as my present application.

Condenser 48 is so proportioned relative to condenser 4! and resistance 42 that the voltage applied to the grid of discharge device 4| is shifted in phase with respect to that applied to the anode of discharge device 4|. That is, the voltage of condenser 28 is displaced approximately degrees from the total voltage of the oscillating circuit, that is, the voltage across 15 tuning condenser 32, and is approximately in phase with the voltage between the anode of discharge device 4| and ground. By proper proportioning of condensers 41 and 48, and resistance 42, a substantial shift in phase between the voltage applied to thegrid and that applied to the anode may be effected. In a particular instance this shift was 63 degrees at a particular frequency, but any desired shift may be produced. Since the anode current is 180 degrees displaced from the grid voltage, it will be seen that the anode current is shifted in phase with respect to the anode voltage and that this tube operates to draw a reactive component of plate current, and, hence, it has the nature of a reactance. With the circuit shown employing condenser 48, the discharge device 4| operates as a capacitive reactance across the winding Of course by proper phasing of the voltage on the grid, as for example by substitution of an inductance for the condenser 48, this discharge device may be caused to operate in the nature-of an inductive reactive. The magnitude of the reactance produced by this discharge device is variable dependent upon the unidirectional potential applied to the grid and hence upon the potential of the automatic frequency control conductor.

It will thus be seen that with switches I6 and 24 adjusted to their righthand position for operation in the broadcast band the automatic frequency control tube operates to control the frequency of the oscillator by variation of the effective reactance in shunt with the winding this effective reactance of course being reflected into the oscillatory circuit and affecting the frequency of the oscillator. If the intermediate frequency shifts from the value to which windings 3! and 38 aretuned, as for'example by reason of the variation of condenser 3| during the tuning operation, the potential on the automatic frequency control conductor 40 increases positively or negatively with respect to ground in accordance with the variations in frequency of the intermediate frequency currents. This variation causes a corresponding variation in the effective reactance produced by discharge device 4| which in turn causes a compensating effect upon the frequency of the oscillator tending to maintain the intermediate frequency constant.

With the switches l6 and 24 in their lefthand position the anode circuit of control electron discharge device 4| is not directly coupled to the oscillatory circuit of the oscillator and has no direct effect upon the reactance of that circuit. Its anode circuit, however, includes resistances 20 and 46 which also are included in the anode circuit of the oscillator. Variation of the unidirectional potential applied to the grid of control tube 4| thus causes a variation in current through resistances 20 and 46 and a corresponding change in the potential applied to the anode of the oscillater. This, in turn, affects the frequency of the oscillator.

An oscillator of the type shown employing the coupling coils l9 and 21, as commonly employed, is generally unstable in frequency with respect to variation of anode voltage, and in accordance with my invention, I utilize this instability to produce the desired automatic frequency control action in one or more of the high frequency bands. The instability of oscillators of this type operating at a frequency above approximately nine megacycles is generally sufficient for the purposes of my invention. Added instability, as for operation at lowerfrequencies may, of course,- if desired, be

produced by any of the. usual expedients such as reduced coupling between the anode and grid circuits. The variation of the anode voltage produced by variation of current in the anode of discharge device 4| and resistances 2|] and 46 is in accordance with my invention, utilized to effect the desired automatic control of the oscillator frequency.

As an example of the operation of my device, the oscillator frequency may normally be greater than the signal frequency by an amount sufficient to produce the desired intermediate frequency when the receiver is tuned exactly to a desired signal. The oscillator may be one in which the frequency increases with increase in applied anode voltage Now let it beassumed that the intermediate frequency, for one of the several reasons which occur in the operation of the device, is greater than the frequency to which the circuits 28, 52 and 31, 53 are tuned. The voltage on diode 35 may then exceed that on diode 36 with the result that a positive voltage appears on the autom-atic frequency control conductor 40. This positive voltage applied to the grid of discharge device 4| causes an increase in current through resistors 26 and 46 and hence reduces the voltage applied to the anode of the oscillator. This, in turn, reduces the oscillator frequency and hence the intermediate frequency. It is thus seen that the effect of discharge device 4| is to maintain the oscillator frequency at the proper value to produce approximately the frequency to which the intermediate frequency circuits are tuned.

Of course, the circuits must be so arranged as to produce the same compensation in all of the bands in which automatic frequency control is employed. As above stated, discharge device 4|, in the broadcast band, acts in the nature of a capacitance across winding ll of the oscillator. Increase in this effective capacitance, which occurs in response to positive voltage on conductor 40 likewise tends to reduce the frequency of the oscillator. Thus, increase in the intermediate frequency in either the short wave, or the broadcast band, above the correct value tends to reduce the frequency of the oscillator and thereby tends to restore the intermediate frequency to a satisfactory value.

It will thus be seen that in accordance with my invention the discharge device 4| may be employed in the broadcast band, for example, to control the frequency of the oscillator by variation of the reactance of the oscillator frequency determining circuit and that it may be employed in one or more of the high frequency and short wave bands to effect automatic frequency control by variation of one of the operating potentials of the discharge device.

It will, of course, be understood that my invention is not limited to variation of the anode voltage of the discharge device this means having been shown as preferred when the pent-agrid converter form of oscillator and first detector are employed. It will, of course, be understood that this frequency control may be effected by variation of any of the operating voltages of the oscillator, the variations of which affect the frequency produced. Any of the grid voltages such as the control grid, screen grid, or suppressor grid voltage may be employed if the discharge device employed in the oscillator be one employing such electrodes. This manner'of effecting the control may be preferable where an electron discharge oscillator separate from the first detector is employed.

This manner of employment of discharge device 4| in the short wave bands, or band, is decidedly advantageous since it does not limit the operating range of the oscillator. It does not in any wise affect the tuning range of the oscillatory circuits which are employed in the short wave bands. At the same time the additional switching which would be necessary were the control tube employed to control the reactance of the oscillatory circuit in the high frequency bands is entirely obviated, the switching in accordance with my invention being no more complicated than would be the case were no automatic frequency control employed at other than the broadcast band. 7

In addition, my invention reduces certain objectionable phenomena which frequently occur in the operation of present day receivers in the short wave bands. For example, in moving the tuning control through the position of resonance with the signal in one direction it has been noted that the signal first gradually comes in and then tends to hold on over a certain region of movement of the tuning control and then suddenly disappears altogether. In moving the tuning control in the opposite direction, the signal suddenly reappears but at a different position of the tuning control, nearer to the position of resonance with the signal, from that at which it disappeared and then gradually fades out. The result is an unsymmetrical tuning effect with respect to variation of the tuning control through resonance.

It has also been noted that if the set be tuned for maximum response during the presence of a strong signal and the signal then fades to some extent, it completely disappears, or a different and adjacent signal may be received. These undesired effects are largely obviated by my invention since when the tuning control is moved toward the region of resonance from either direction, the signal suddenly appears and remains until the tuning control has passed through resonance, when it again suddenly disappears,

Switch 5!! is employed to ground the automatic frequency control conductor thereby to disable the automatic frequency control circuits.

While I have shown a particular embodiment of my invention it will be understood that I do not wish to be limited thereto since different modifications both in the circuit" arrangement and in the instrumentalities employed may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electron discharge oscillator having a frequency determining circuit, means to alter the reactance of said circuit for operation in different bands, means to supply operating voltage to said electron discharge oscillator, a source of variable electromotive force, and means responsive to variations in said variable electromotive force to control the frequency of said oscillator, said means including means to effect said frequency control by varying the effective reactance of said circuit in one band and by varying said operating voltage in another band.

2. In combination, anelectron discharge oscillator having a frequency determining circuit, means to alter the reactance of said circuit for operation in different bands, means to supply operating voltage to said electron discharge oscillator, an electron discharge device having an anode, a cathode, and a grid, a source of variable electromotive force connected between said grid and cathode, and means utilizing the space between said anode and cathode as a variable reactance to control said frequency of said oscillator in one band in accordance with said variable electromotive force and to utilize said space between said anode and cathode as a variable resistance to vary said operating voltage in another band.

3. In combination, an electron discharge oscillator having a frequency determining circuit, means to alter the reactance of said circuit for operation in different frequency bands, means to supply operating voltage to said electron discharge oscillator, the frequency produced by said oscillator being dependent upon the magnitude of said operating voltage in at least one of said bands, and means to vary said operating voltage in said one band and the reactance of said frequency determining circuit in a different band thereby to control the frequency of said oscillator.

4. In combination, an electron discharge oscillator having a frequency determining circuit, means to alter the reactance of said circuit for operation in different frequency bands, means to supply operating voltage to said electron discharge oscillator, the frequency produced by said oscillator being dependent upon the magnitude of said operating voltage in at least one of said bands, an electron discharge device coupled to said circuit to control the reactance thereof during operation in one of said frequency bands, and

means utilizing said discharge device to control the magnitude of said operating voltage in a different frequency band.

5. The combination in a superheterodyne receiver of a. local oscillator having a frequency determining circuit, means to combine the oscillations produced by said local oscillator with the received oscillations and to reproduce the signal from currents resulting from such combination, means to alter the frequency determining circuit for operation in different bands, means to supply operating potential to said local oscillator, and means responsive to said resulting currents to control the frequency produced by said local oscillator in any band, said means comprising means to vary the effective reactance of said circuit in one band and to vary said operating potential in another band.

6. The combination, in a superheterodyne receiver, of a local oscillator having a frequency determining circuit, means to combine the oscillations produced by said local oscillator with the received oscillations and to reproduce the signal from currents resulting from such combination, means to alter the frequency determining circuit for operation in different bands, means to supply operating potential to said local oscillator, the frequency of the local oscillator being dependent upon the magnitude of said operating potential, means to tune said circuit to anyfrequency in any band, and means responsive to said resulting currents to control the frequency produced by said local oscillator to produce resulting currents of constant frequency in any band irrespective of the accuracy of tuning of 'said circuit by said last means to a desired frequency, said means comprising means to vary said operating potential in one band and the reactance of said circuit in another band.

7. The combination, in a multiband, variably tuned superheterodyne radio receiver, employing the same electron discharge local oscillator in the different bands, means responsive to variations in the intermediate frequency of said receiver to regulate the frequency of said oscillator thereby to maintain said intermediate frequency constant during variation of the tuning of said receiver through a range in proximity. to resonance with a desired signal, said means including means to regulate the anode voltage of the oscillator in one band and to regulate the reactance of the oscillatory circuit of the oscillator in a different band.

8. The combination, in a multiband variably tuned superheterodyne radio receiver, employing the same electron discharge local oscillator in the different bands, said local oscillator having a frequency determining circuit and an anode cathode circuit, said anode cathode circuit including a resistance and source of operating potential, the frequency produced by said local oscillator being dependent on said frequency determining circuit and, in at least one band, on the potential supplied between said anode and cathode, a control electron discharge device having an anode, a grid and a cathode, said resistance and source of operating potential being connected between the anode and cathode of said control electron discharge device, and means operable in a band other than said one to couple said frequency determining circuit to both the grid and anode of said control electron discharge device to produce voltages thereon such that a reactive current flows between said anode and cathode thereby affecting the frequency determined by said frequency determining circuit in said other band, and means responsive to variations in the intermediate frequency of said receiver to control the unidirectional potential on said grid thereby to control the potential supplied between said anode and cathode of said local oscillator.

9. In combination, an electron discharge oscillator having a circuit tunable to a selected frequency in a frequency range, means to supply an operating voltage to said electron discharge oscillator, and means for controlling the frequency of said oscillator over a limited frequency range which includes a selected frequency, said last named means being arranged to control the tuning of said tunable circuit when said oscillator is operating within a predetermined portion of its frequency range and to control the magnitude of the operating voltage supplied by said first named means when said oscillator is operating within a second predetermined portion of its frequency range.

10. In combination, an electron discharge oscillator having a circuit tunable to a selected frequency in a frequency range, a source of operating voltage for said'oscillator, means responsive to the departure of said oscillator from a selected frequency for developing a control potential, and means responsive to said control potential for restoring said oscillator substantially to said selected frequency, said last named means operating either to change the tuning of said tunable circuit when said oscillator is operating within a predetermined portion of its operating range or to change th magnitude of operating voltage supplied to said oscillator when said oscillator is operating within another portion of its operating range,

11. The combination, in a radio receiver tunable over a plurality of frequency bands, of means for producing from received signal oscillations other oscillations of intermediate frequency, said last named means including a local oscillator whose output frequency is controlled both by a resonant circuit and by the magnitude of an operating potential supplied to said oscillator, and means for maintaining substantially constant at a predetermined value the frequency of said intermediate frequency oscillations, said last named means being responsive to the frequency of said intermediate frequency oscillations to vary the resonant frequency of said resonant circuit while said receiver is tuned throughout one frequency band and to vary the magnitude of said operating potential while said receiver is tuned throughout a second frequency band.

GEORGE W. FYLER. 

